Pasteurizing paints and method for pasteurizing paints

ABSTRACT

Disclosed herein are methods for pasteurizing architectural coating compositions using heat, radiation or other energy sources without additionally polymerizing the compositions and storing same.

FIELD OF THE INVENTION

This invention generally relates to paints that have been pasteurized toremove or sufficiently reduce the amount of bacteria, fungi, yeastsand/or other biological agents in paints and to method for pasteurizingsame.

BACKGROUND OF THE INVENTION

Due to environmental and health concerns, there has been a movementtoward reducing the amount of volatile organic compounds (VOCs) inpaints, stains, and other coating compositions, which evaporate into theenvironment upon paint film formation. Additives to paints thatfacilitate or impart desirable paint properties, such as better filmcoalescence, better resistance to blocking, better film durability,better physical and chemical scrub resistance, and tougher coatings,among others, also contain VOCs. The evaporation of VOCs often resultsin undesirable aromas, and exposure to such fumes, particularly in areasthat are not well ventilated, remains a health concern. Thus, lessvolatile or non-volatile additives, as well as colorants, that impartcomparable (or superior) properties to the paints have been used toreplace higher VOC additives. The quest for low VOC paints or a better“green paint” is discussed in a New York Times newspaper articleentitled “The Promise of Green Paint” (Kershaw, Sarah, The New YorkTimes, May 15, 2008, p. F6), which is incorporated herein by referencein its entirety.

The reduction of VOC in paints, stains and other coatings and inadditives, however, has produced environmentally friendly paints thatare more inviting to bacteria, algae, yeasts, fungi and other biologicalagents that thrive in an aqueous environment. These biological agentsgrow and die in paint cans and containers, and often impart anunpleasant odor and render paints unusable for its intended purpose, andcan cause viscosity loss, discoloration, gassing, frothing,sedimentation and pH changes. Biological agents also present potentialhealth issues. Certain biological agents, such as algae and molds, maygrow on dried paint films covering walls or other substrates.

Biocides have been used in aqueous paints or stains to controlbiological agents inside cans and containers. Some of the biocides mayremain on the dried paint film to control algae and molds. However,there is a need to minimize the amount of biocides in aqueous paints ordried paint films while preventing the unimpeded growth of biologicalagents.

SUMMARY OF THE INVENTION

Hence, the invention is directed to a method for pasteurizing paintswith an energy source, such as heat, gamma ray radiation, otherirradiations, electron beam, etc. to kill any biological agents that mayhave been introduced into the paints before being poured into paint cansor containers and sealed for transportation or storage before the paintsare used by the consumers. The present invention is also directed tostoring the paint cans and containers in climate controlled environmentsto discourage the growth of biological agents while in storage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bar graph illustrating the experimental results from Example7;

FIG. 2 is a bar graph illustrating the experimental results from Example8; and

FIG. 3 is an X-Y graph showing a relationship between pasteurizingtemperature and pasteurizing time duration.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, paint or paints include aqueous or water-based paintcompositions, stains or other architectural coatings. Paint film(s)means paint(s) that have been applied on a surface or substrate, and aredried or the latex particles in the paint(s) have cross-linked to form afilm.

The energy sources for pasteurization preferably include heat or anotherthermal source, and radiation including but not limited to irradiationwith alpha or gamma rays, microwave rays, electron beams, and any othersource of radiation. The present invention is not limited to anyparticular source of energy as long as that energy source can eradicatebiological agents and minimally affect the paints.

Water-based latex architectural coatings, such as paints, stains, otherhousehold and industrial coatings and paints, have become moreenvironmentally friendly. This means that modern day architecturalcoatings have less VOCs in them and have additives and colorants thatalso have low VOCs. The reduction in VOCs have rendered thearchitectural coatings more inviting to biological agents, such asbacteria and fungi in the water phase and algae and certain fungi, e.g.,molds, in the dried film phase. One solution is to add biocides to thearchitectural coatings at the latex formation stage, at the pigmentdispersion stage, where pigments are dispersed with surfactants,dispersants and water, and/or the let-down stage where the aqueouslatex, the pigment dispersion and additives are combined. The paints arethen placed in cans and containers for storage and shipping. Colorants,which may contain their own biocides, are added later at the retailstores to achieve the paint colors that the consumers purchased.

While biocides are useful to preserve paints and other architecturalcoatings and are useful in the dried paint film to help prevent thegrowth of biological agents, some environmentally conscientiousconsumers have expressed a desire for biocide-free or biocide-reducedpaints. However, without biocide or with reduced biocides biologicalagents could thrive in paints or paint films.

One aspect of the present invention is to pasteurize the paints andother architectural coatings so that the growth of biological agents iseither obviated or limited in the absence of biocide or with reducedbiocides. In a preferred embodiment, the paints are pasteurized with anenergy source, preferably heat or radiation sources, during themanufacturing process to significantly reduce the population ofbiological agents, and then stored in containers, such as one-gallon orsmaller cans or five-gallon pails. Then paint containers are then storeduntil sold to the customers. In most situations, the paint containersare shipped to and then stored at paint distribution centers and thenshipped and stored at retail stores before being purchased by consumers.

In another embodiment, the paints are pasteurized by the energy sourceafter they are stored in their containers. Entire filled paintcontainers are pasteurized by subjecting them to the energy source. Anadvantage of this embodiment is that the empty containers, which may bea source of biological agents, are also pasteurized along with thepaints contained therein. Alternatively, the empty containers can bepasteurized separately before they are filled with pasteurized paints.The duration of the paints' exposure to the energy source should be longenough to substantially eradicate the biological agents.

The following biological agents can be found in paints:

-   -   i. Bacteria: pseudomonas species, including Pseudomonas        aeruginosa; gram negative rod bacteria; Enterobacter aerogenes;        Sphingomonas paucimobilis; etc.    -   ii. Yeasts: Candida lambica and Yarrowia lipolytica, etc.    -   iii. Fungi (molds): aspergillus species, acremonium species,        geotrichum species and penicillium species, etc.        In some of the examples or experiments discussed below, an        inoculum comprising the above listed biological agents is        introduced into paints or paint containers and the biological        agents are allowed to grow. Thereafter, the paints are        pasteurized, and the paints are re-tested to determine the        residual concentration of biological agents (if any). In other        examples or experiments, commercial paints with biocides that        were overwhelmed by one or more known biological agents are        pasteurized and re-tested to determine whether contaminated        paints can be returned to the commercial conditions and be        suitable for sale.

Pseudomonas aeruginosa or P. aeruginosa was found in some contaminatedpaints. This bacterium is commonly found in wet and warm environments,such as swimming pools and hot tubs. It has been reported by researchersfrom schools of medicine and public health that P. aeruginosa can growin the range of 25° C. to 42° C. but can be killed at temperature of 60°C. and up to 70° C. for a duration of about 30 minutes. P. aeruginosadoes not grow but does not die at temperature of 10° C. up to 15° C. or20° C. These results were reported by A. Tsuji, Y. Kaneko, K. Takahashi,M. Ogawa and S. Goto, “The Effects of Temperature and pH on the Growthof Eight Enteric and Nine Glucose Non-Fermenting Species ofGram-Negative Rods,” Toho University School of Medicine, Department ofMicrobiology, J. Microbio. Immunol, Vol. 26(1), 15-24, 1982 at pp.15-24, which is incorporated herein by reference in its entirety.

Tsuji et al. also reported the effects of heat on the followingbacteria.

TABLE 1 Survival Growth Peak Bacteria Species T(° C.)^(‡) T(° C.)^(†)T(° C.) 1 E. Coli 10-50 18-47 40 2 K. pneumoniae 10-50 16-48 36 3 S.marcescens 10-50 19-41 35 4 P. aeruginosa 10-50 25-42 37 5 P. cepacia10-50 28-37 34 6 P. fluorescens  10-40¹ 25-32 30 7 P. maltophilia 10-5022-39 34 8 A. xylosoxidans  10-40² 28-37 35 9 A. calcoaceticus 10-5020-45 38 10 A. faecalis  10-40² 28-37 36 11 F. meningosepticum 10-5024-37 33 12 Moraxella  10-40³ 23-35 30 13 P. mirabilis 23-44 37 14 P.vulgaris 22-41 37 15 P. morganii 23-42 36 16 P. rettgeri 24-43 36 17 P.inconstans 22-45 38 (E. is the genus Escherichia; K. is the genusKlebsiella; S. is the genus Serratia; P. is the genus Pseudomonas; A. isthe genus Acinebacter; F. is the genus Flavobacterium.) ^(‡)= survivefor at least 6 hours; survival tests conducted at 10-70° C. atincrements of 10° C. ¹= survive at 50° C. for about 1 hour. ²= surviveat 50° C. for about 4 hours. ³⁼ survive at 50° C. for about 2 hours.^(†)= growth tests conducted at 10-50° C. and the time for growth from10² cells/ml initial concentrations to 10⁷ cells/ml was noted; bacteriagrowths were observed for 48 hours.

All of the tested bacteria were eradicated at temperature of 60° C. or70° C. for duration of 30 minutes. No bacteria survived at 60° C. formore than 2 hours. None survived more than 30 minutes at 70° C.

All of the tested bacteria survived at 10° C. but did not grow.Otherwise, they grow at the reported temperature ranges, and the peak oroptimal growth temperatures are also reported.

Tsuji et al also reported that at pH from 6.4 to 8.2 has little effecton the growth rate of these bacteria. However, S. Bricha, K. Ounine S.Oulkheir, N. El Haloul and B. Attarassi, “Heat Resistance of Pseudomonasaeruginosa in Preparations at the Base of Cucumber, Tomato and Lettuceas Affected by pH and Sodium Chloride,” Ibn Tofail University, Morocco,ISPROMS ISSN: 1994-5108, WJBR Vol. 3, Issue 1, at 1-8, reported that atpH of about 2 a heat resistant strain of P. aeruginosa's heat resistanceis diminished at temperature of 63° C., but the heat resistance of P.aeruginosa at pH of 4.5 and 6 is about the same. Bricha el al. alsoreported that at low pH sodium chloride salt at 2-6% may protect thebacteria. Bricha et al. is incorporated herein by reference in itsentirety.

The present inventive pasteurization method comprises:

(i) heating (or applying a radiation source to) the paint toward apasteurization temperature (or pasteurization condition),

(ii) keeping the exposure time sufficiently long to ensurepasteurization,

(iii) cooling the paint down to an ambient temperature or lower, and

(iv) storing the pasteurized paint until being purchased and used by theconsumers. Preferably, the eradication in step (i) is up to a 3-log(99.9%) reduction, preferably a 4-log (99.99%) reduction and morepreferably a 5-log (99.999%) or more reduction.

Preferably, the energy source is heat and heat is applied, as heated airin ovens, in hot water baths or through heated pipes or vessels, to thebiological agents to raise the temperature of the paints to be higherthan the growth temperature range of the biological agents andpreferably more than about 49° C. or about 50° C. for at least 6 hoursfor paints substantially without biocide or for at least 2 hours forpaints with biocides in an air oven; or about 60° C. for at least about75 minutes for paints substantially without biocide and for at leastabout 30 minutes for paints with biocides in an air oven; or about 70°C. for less than 30 minutes, preferably between 1 minute and 30 minutes,preferably between 1 minutes and 15 minutes for paints substantiallywithout biocide, and preferably less than 5 minutes or less than 4minutes or less than 3 minutes for paints with biocides in an air oven.As shown below, the pasteurization time decreases when hot water bathsare used.

Alternatively, other energy source such as radiation as discussed abovecan be used. In another embodiment, the paints are pasteurized byradiation, e.g., gamma rays or gamma radiation. Paints are pasteurizedby absorbing less than or about 15 kilogray (kGy), preferably less thanor about 10 kGy, preferably less than about 5 kGy or more preferablyless than about 3 kGy.

Preferably the storage of paint in step (iii) includes storing the paintcontainers in an environment that bacteria, if present, do not grow. Asdiscussed above in Table 1, at 10° C. a large number of bacteria do notgrow. Additionally, the temperature growth range of these bacteria isabove 15° C., and very few bacteria would grow at temperature at 20° C.Hence, preferably the paints is stored at temperature of 20° C. (68° F.)or lower, more preferably at temperature of 15° C. (59° F.) or lower, ormore preferably at temperature of 10° C. (50° F.) or lower. Thesepreferred storage temperatures can be achieved with conventional airconditioning technology. Additionally, it is preferred that duringtransportation the paints are also kept at these temperature ranges.

Yeast cells begin to die at temperature greater than 50° C. and mostwould die at temperatures from about 55° C. to about 60° C. It is wellknown to bakers that yeasts when added to water that is too warm arekilled and the dough won't rise. At temperatures of 10° C. or lower,yeasts would not grow. Yeasts grow in the temperature range from about27° C. to about 32° C. depending on the species. Hence, yeasts have asimilar dormant-growth-death temperature profile as the bacteriadiscussed above. Hence, yeasts can be eradicated and/or controlled bythe inventive pasteurizing method including storage and transportation,described above.

Molds including mildew, fungi, and common molds exist in the sametemperature range (and relative humidity) that supports human life.Hence, mold and mold spores are ubiquitous in our environment. Molds cangrow in temperatures between 4° C. and 38° C. (40°-100° F.). Below 4°C., molds are in a dormant state and are revived when the temperaturewarms up with the proper relative humidity. Some molds survivetemperature as high as 38° C. or higher. The dormant-growth-deathtemperature regime for several molds and spores has been reported, asshown below. See http://www.thermapure.com/envinmental-services/mold/.

TABLE 2 Mold species Lethal T(° C.) Duration (min) Alternarie altermata63 25 Aspergillus fumigatus 65 30 Aspergillus niger 63 25 Chaetomiumglobosum 57 10 Cladosporium herbarum 50 10 Stachybotrys chartarum 60 30While some lethal temperatures are slightly higher than 60° C. for someof the mold discussed above, the time duration to kill is significantlyshorter. The present inventors have discovered that at 60° C. but forlonger time duration, most molds can be killed. Hence, molds can beeradicated and/or controlled by the same inventive pasteurizing methodincluding storage and transportation, described above.

On the other hand, the heat or radiation treatment should not exceed thetemperature/radiation level and duration that would initiate additionalpolymerization or other deleterious effects within the aqueous paint.Latex particles due to the added heat or radiation energy can cross-linkto each other while in solution thereby producing larger latex particlesthat can negatively affect the quality of the paint film. In some of theexamples discussed below, the present inventors have shown that theinventive pasteurization process does not appreciably alter the propertyof the paints or the paint films.

The inventive pasteurization method may include flash pasteurization,where paint is heated to a relatively higher temperature but for ashorter time period. Flash pasteurization typically takes placeimmediately after the paint is produced or as the last step inproduction at the factory before it is stored in containers. Paint canbe heated in a heating coil for maximum heat transfer for the requisitetime and is then quickly cooled, e.g., with forced convection overcooling fins, to remove the heat. In one example, the paint is heated toa range of about 71° C.—about 74° C. (160° F.-165° F.), preferably about71° C.—about 73° C. (160° F.-163.5 F), more preferably about 71.5° C.—about 72° C. (161° F.-162° F.) for less than about 4 minutes or lessthan about 3 minutes, preferably less than about 2.5 minutes, morepreferably less about 2 minutes or about 1.5 minutes.

The above method has been used on tainted paints, i.e., paints thatcould not be commercialized due to biological agent contamination. Theheat treatment sufficiently removed the biological agents and theformerly tainted paints could return to the warehouse/distributioncenter. Tainted paints that are already stored in containers can bepasteurized in an air oven or in a heated bath of water or otherliquids. As discussed herein, commercial paints contain biocides addedduring the manufacturing process.

EXAMPLES Example 1

Pint size paint cans containing a commercial premium interior flat paintthat contains a customary amount of biocides and was contaminated withvarious bacteria as identified using a dip slide test, which is ahygiene contact slide used to assess the microbiological contaminationof surfaces or fluids. Suitable dip slide tests for hygiene monitoringinclude a plastic two-side testing device commercially available asDifco™ Hycheck™ Yeasts and Molds with TTC (triphenyl tetrazoliumchloride as a redox indicator) from Becton Dickenson. These hygienecontact slides are used to assess the microbiological contamination ofpaints in all examples. Side 1 of a two-sided plastic paddle (akacontact slide) attached to the closure top for the plastic vial iscoated with a pink agar recommended for the selective isolation ofyeasts and molds (fungal contamination) from environmental materials andfoodstuffs. Side 2 is coated with a clear colorless agar mediumrecommended for microbial limits testing to give a total aerobicbacterial count. Bacterial colony growth is checked after 24, 48 and 72hours or longer incubation at 30° C., discussed in literature insertsupplied with slides and incorporated by reference in its entirety.Testing by this technique does not differentiate types of bacteria, butrather shows all bacteria that are present, and in the case of thiscontaminated commercial paint, the bacteria have overwhelmed thebiocides. The units for the dip slide or Hycheck™ tests are indicativeof the number of bacteria or yeasts/molds colonies. Level 1 has about10³ colonies; level 2 has about 10⁴ colonies; level 3 has about 10⁵colonies; and level 4 has about 10⁶ colonies. The colonies are notactually counted, but are estimated based on comparisons tophotographs/pictures provided by the manufacturers. Bacteria are ratedlevel 1, 2, 3 or 4 (max), and molds/yeasts are rated level 1, 2 or 3(max).

The contaminated paint cans were submerged in a hot water bath set at67° C. The temperature of the paints was measured by a digitalthermometer. The lag time, i.e., the time for the temperature inside thepaint can(s) to reach a steady state of about 65.5° C., which isslightly below the hot water bath's temperature, was recorded. Thesepaint cans were then incubated at 30° C. for 72 hours to check forbacterial growth. Bacterial growth was checked after 24, 48 and 72hours.

Time in Pasteurized Time, Bath, hr:min @ Lag Time, minutes @ Sample 67°C. hr:min 65.5° C. A 0:0  0:0  0 (control) B 1:52 1:15 37 minutes C 1:301:15 15 minutes D 1:45 1:15 30 minutes E 2:15 1:15 60 minutesControl paint A experienced significant bacterial growth. Samples B-Ehad no bacterial growth after 24 hours and after 72 hours. No sampleexhibited mold/yeast growth. To determine whether the pasteurizationaffected the physical properties of aqueous paints and paint films, acontaminated sample was compared with a pasteurized sample that has beenheated for 60 minutes in the same bath excluding lag time. The resultsare produced below.

Contaminated Pasteurized Property Paint Paint Viscosity (KU) 101.2 101.1Viscosity (ICI) 1.396 1.333 Gloss 60° 2.3 2.3 Gloss 85° 2.6 2.7 FlowLeveling, 1(worst)-10(best) 6 6 Blocking, 1-5(best) 5 5 WaterSensitivity, 1-5(best) - 1 min 2 2 Water Sensitivity - 2 min 1 1 WaterSensitivity - 3 min 1 1 Water Stain, 1-5(best) 3.5 3.5 Scratch WetAdhesion, 1-5(best) - 4 4 1 min Tape Wet Adhesion, 1-5(best) - 2 5 5 minTape Wet Adhesion - 5 min 5 5 Tape Wet Adhesion - 10 min 5 5 Scrubcycles, initial/complete break 385/529 345/465 in film Scrub cycles toremove proprietary 23.0/62.0 23.0/61.0 carbon black stains Sag, mils 1212The wet and dried properties of the contaminated paint and thepasteurized (formerly contaminated) paint are very comparable, exceptfor a small drop in the scrub test. Hence, the inventive pasteurizationdid not negatively affect the paint. The pasteurization alsosignificantly reduced the odor caused by the contamination.

Example 2

Six vials, each containing 21.5 grams of contaminated paint used inExample 1, were pasteurized in a hot water bath maintained at 71° C. Atthis relatively small volume, the lag time or time to reach thepasteurized temperature was 2 minutes. The vials were pasteurized fordifferent amount of time, i.e., 1, 2, 4, 8, 16 and 32 minutes excludinglag time or 3, 4, 6, 10, 18 and 34 minutes including lag time. Afterpasteurization, the vials were immediately submerged in a cold waterbath at 12° C. to stop the pasteurization. All six vial samples testednegative for bacterial growth after 72 hours of incubation at 30° C. Thecontrol sample tested positive. All samples tested negative for mold andyeast.

Example 3

The results from Example 2 indicated that a short duration of 3 minutesincluding lag time was sufficient to eradicate the bacteria. ThisExample explored shorter time durations. Another six vials eachcontaining 21.5 grams of the same contaminated paint were pasteurizedwith three at 63° C. for 1, 2 and 4 minutes including lag time and threeat 71° C. at 0.75, 1.5 and 3 minutes including lag time. The samplepasteurized at 71° C. for 3 minutes duplicates the shortest pasteurizedtime from Example 2. These six samples and a control were applied tosubstrates and incubated for 48 hours at 30° C. Digital photographsafter the incubation show that pasteurization at 71° C. for 3 minuteskilled most of the bacteria and pasteurization at 63° C. for 2 and 4minutes also killed a significant amount of bacteria.

Example 4

Since commercial paints are sold mostly in gallon-size cans orfive-gallon tubs, the present inventors also conducted experiments withthe larger paint containers. The heat transfer coefficient of paint isrelatively high and the heat capacitance of air in commercial ovens ismuch lower than that for water thereby causing significant lag time forthe paints to reach the heating/pasteurizing temperature from ambient orinitial temperature. Individual gallon size paint cans of contaminatedcommercial paint were heated in an air oven at 80° C. for 5½ hours. Thepaint temperature only reached 67° C. This means that the paint has notyet reached its steady state oven temperature, and the thermal energyfrom the oven was not sufficient after 5½ hours to bring the temperatureof the paint to the temperature of the oven.

Example 5

Additional experiments were conducted to determine the lag time forheating a box containing four 1-gallon paint cans of the contaminatedcommercial paints, which tested positive for bacteria by Hycheckincubation, arranged in a 2×2 pattern to reach pasteurizing temperaturein an air oven. Boxes of four paint cans are typically sold to and byretail stores. The present inventors discovered that the lag time may beup to 7½ hours for the temperature of the paint inside the cans to reachtarget pasteurizing temperature of about 60° C. In one example, with anoven air temperature holding at 80.6° C. and after 7 hours and 39minutes, the air temperature between the cans was 61.8° C. and the painttemperature in the middle of the can was 54.6° C. In another example,with an oven air temperature at about 100° C. and the temperature on topof the cans at 99.2° C. after about 72 hours, the air temperaturebetween the cans was 73.4° C. and the paint temperature in the middle ofthe can was 67.6° C.

Even though the two samples from Example 5 did not reach their steadystate air oven temperature targeted for pasteurization, the heat treatedpaints were tested for bacterial growth using the Hycheck contact slideincubated at 30° C. for 48 hours and tested negative for bacteria.Example 5 shows that the heat energy used to bring up the painttemperature from ambient toward air oven temperature was sufficient toeradicate the bacteria, even though the paint sample did not reach thetargeted pasteurization temperature of 60° C. This result is unexpectedin view of the teachings from Tsuji et al, supra.

Example 6

Boxes containing four one-gallon cans of the commercial contaminatedpaint were heated in the air oven similar to Example 5.

Bacteria and Mold/Yeast Oven Paint Time in Time at Oven after T(° C.)T(° C.) Oven Temperature Incubation Control yes Sample 1 60 60 41.5 hrsabout 10 hrs none Sample 2 70 64.6 16.75 hrs  n/a none Sample 3 70 68.324.5 hrs n/a nonePaint Properties

Viscosity Viscosity Dry Film 85° Dry Film 60° (KU) (ICI) Sheen GlossControl 95.3 1.183 4.3 2.5 Sample 1 95.6 1.362 4.2 2.5 Sample 2 95.61.262 4.2 2.5 Sample 3 95.9 1.225 4.0 2.5Except for a slight increase in the ICI viscosity in the aqueous paint,the dry film properties and the KU viscosity did not significantlychange.

Based on Examples 1-6 and more specifically Example 5, the presentinventors concluded that it may not be necessary to bring thetemperature of the paints to a steady state pasteurizing temperature andhold for a certain amount of time in order to eradicate the bacteria.

Example 7

Paints with substantially no biocides were made and inoculated with aninoculum comprising various bacteria and molds from THOR CHEMIE GMBH.Glass vials with caps containing about 52 grams of the inoculatedbiocide free paints were pasteurized at 49° C. (120° F.) and 60° C.(140° F.) in a heated air oven for varying time periods, as reportedbelow. Two controls were used: a positive inoculated control and anegative control which was not inoculated. Dip slide tests for bacteriawere conducted after 24, 48 and 120 hours of incubation and dip slidetests for molds were conducted after 48 and 120 hours incubation.

Sample (time @ T° F.) 24 h-B 48 h-B 120 h-B 48 h-M 120 h-M A (75 min @120° F.) 0 3 3 0 0 B (90 min @ 120° F.) 0 3 3 0 0 G (120 min @120° F.) 01 2 0 0 H (360 min @ 120° 0 0 1 0 0 F.) J (1380 min @ 120° 0 0 1 0 0 F.)E (+positive control) 0 2 2.5 0 0 F (−negative control) 0 0 0 0 0 K (15min @ 140° F.) 0.5 3 3 0 1 L (30 min @ 140° F.) 0.5 3 3 0 0 M (60 min @140° F.) 0 2 2 0 0 C (75 min @ 140° F.) 0 0 0 0 0 D (90 min @ 140° F.) 00 0 0 0 E′ (+positive control) 1 3 3.5 0 0 F′ (−negative control) 0 0 00 0The data shows that pasteurization at 120° F. is effective againstbacteria and mold growth, but some bacteria were present after 120 hoursof incubation at 30° C. Pasteurization at 140° F. for between 60 minutesand 75 minutes is effective for both bacteria and mold. The data alsoshows that pasteurizing at 140° F. takes less time than pasteurizing at120° F. The negative controls show that there was no background or othercontamination in the experiments and the positive controls show thatbacteria would be present without pasteurization. The data also suggestsstrongly that flash pasteurization can be realized with even higherpasteurizing temperature, preferably below polymerization temperature ofthe latex particles, for a very short time, as discussed above. The datafrom Example 7 is graphed as shown in FIG. 1.

Example 8

Commercial paints with conventional biocides that were contaminated weretested in glass vials. Each glass vial holds about 52 grams of thecontaminated commercial paints. The vials were pasteurized at 49° C.(120° F.) and 60° C. (140° F.) in a heated air oven, cooled andincubated similar to those in Example 7. The results are as follows:

Sample (time @ T° F.) 24 h-B 48 h-B 120 h-B 48 h-M 120 h-M A (120 min @120° 0 0 0 0 0 F.) B (360 min @ 120° 0 0 0 0 0 F.) C (1380 min @ 120° 00 0 0 0 F.) D (15 min @ 140° F.) 0 4 4 0 0 E (30 min @ 140° F.) 0 0 0 00 F (60 min @ 140° F.) 0 0 0 0 0 G(+positive control) 0 4 4 0 0Example 8 shows that with biocides in the paint the pasteurized time andtemperature can be reduced. Heating at 120° F. for 2 hours (120 minutes)is sufficient to reduce bacterial and mold growth, and heating at 140°F. for 30 minutes is sufficient to reduce bacterial and mold growth. Thedata from Example 8 is graphed as shown in FIG. 2. Compared to Example7, the biocides that were overwhelmed by the bacteria and/or mold arereactivated when heated and combined with the pasteurization provide asynergistic effect.

Example 9

Commercial paints with conventional biocides that were contaminated weretested in ½ pint cans containing about 270 grams of paint. The cans wereheated in an air oven at 60° (140° F.) for a number of hours todetermine whether the overwhelmed biocides can be revived. Samples wereheated for 3 hours, 6 hours, 16.5 hours and 25 hours. A positivecontrol, i.e., with additional inoculation, and a negative control,i.e., without additional inoculation, were also checked for bacterialgrowth. Both controls exhibit significant bacterial growth (4 units)after being incubated for 48 hours, 72 hours and 144 hours. None of thepasteurized sample shows any bacteria growth after 24 hours, 48 hours,72 hours and 144 hours of incubation. No mold was detected in thepasteurized samples or the controls after being incubated for 48 hours,72 hours and 144 hours.

The pasteurization regime for paints with biocides gathered fromExamples 1-9 can be described as follows. The data is selected in partbased on the relative small sizes of the paint samples.

Time (minutes) Temperature ° C. Source 3 71 Exs. 2 & 3 15 65 Ex. 1 30 60Ex. 8 120 49 Ex. 8The pasteurization time-temperature relationship graph is shown in FIG.3. It is noted that the time duration can be longer than the timereported in this Table as shown in the Examples above, and could beless, e.g., 25% less than the reported time. The graph in FIG. 3 canalso be presented on a semi-log graph, i.e., log₁₀(Temperature) vs.time. This table also shows feasibility of flash pasteurization,discussed above.

The pasteurization regime for paints without biocides gathered fromExamples 1-9 can be described as follows.

Time (minutes) Temperature ° C. Source 75 60 Ex. 7 360 49 Ex. 7It is noted that the time duration can be longer than the time reportedin this Table as shown in the Examples above, and could be less, e.g.,25% less than the reported time.

Example 10A

Commercial paints with conventional biocides that were contaminated werepasteurized with gamma ray radiation. Gallon sized cans were exposed toa various level of gamma radiation, i.e., 3, 5, 10 and 15 KG (kilogray).Some cans were treated with heat at 45.5° C. (114° F.) and at 74.4° C.(166° F.) for comparison, discussed further below in Example 10B. Thepresent inventors discovered that gamma radiation is effective againstbiological agent contamination while the controls show growth, as shownin the Table below. Additionally, high shear and low shear viscosities(measured in KU and poise) are affected by the radiation. The tintstrength is decreased more with heating than with gamma radiation. Thecontrast ratio is substantially unchanged. Heat and gamma radiationappear to have increased the foam in the paint sample, i.e.,pasteurization may have negatively affected the defoamer additive withthe gamma radiation having a greater effect.

γ level Bact. WPG Visco. ICI pH Gloss Sheen Tint C/R Foam Control 0 211.12 94.1 1.25 8.31 2.5 4.5 100.52 0.967 17  1 3 0 11.08 93.5 1.2468.32 2.6 4.2 100.52 0.956 45  2 3 0 11.09 91.9 1.212 8.32 2.7 4.7 100.460.950 27  3 5 0 11.05 89.3 1.231 8.27 2.5 4.7 101.78 0.968 45  4 5 011.10 90.7 1.334 8.36 2.4 4.4 100.55 0.956 45  5 5 0 11.08 90.6 1.2378.30 2.4 4.5 100.91 0.966 45  6 10 0 11.05 87.6 1.117 8.40 2.4 4.3101.31 0.955 45  7 10 0 11.07 88.8 1.169 8.34 2.5 4.2 100.99 0.964 45  810 0 11.10 88.4 1.081 8.31 2.5 4.4 101.53 0.958 45  9 15 0 11.02 86.40.977 8.28 2.4 4.5 101.32 0.961 45 10 15 0 11.05 87.5 1.029 8.31 2.5 4.4101.81 0.945 45 11 15 0 11.08 87.6 1.044 8.35 2.4 4.3 100.7 0.961 45

-   -   gamma (γ) level is measured in kilogray (KGy), which is a SI        unit equivalent to 1,000 Joules absorbed by 1 kg of matter; the        amount of radiation absorbed by the paints relates to the        strength of the source of radiation, the distance between the        source and the paints and the time duration of exposure.    -   bacteria levels are checked by dip slide tests (Hychecks)        discussed above after a 72 hour inoculation at 30° C.    -   WPG is the weight (lbs.) per gallon of paint    -   Viscosity is measured in KU or Krebs Units; ICI viscosity is        measured in poise    -   Gloss and sheen are paint finishes discussed in commonly owned        U.S. Pat. No. 8,507,579, which is incorporated by reference        herein in its entirety    -   Tint is % tint strength, which is defined as a measure of how        well titanium dioxide can add whiteness to a tinted paint,        described in commonly owned U.S. patent application Ser. No.        14/531,354 “Additives for Improved Hiding and Painting        Compositions Containing Same” filed on 3 Nov. 2014, incorporated        herein by reference in its entirety.    -   Contrast ratio is the ratio of the Y value of the paint over the        painted black region divided by the Y value of the paint over        the painted white region, and described in Ser. No. 14/531,354.    -   Foam is the time in seconds for the foam to dissipate or        disappear.

Example 10B

In sample 12, a pallet of paints was heated in an air oven at 75° C.(167° F.) for 24 hours, then the oven temperature was increased to 80°C. and again to 85° C. at 24.5 hours. A pallet contains 27 boxes of4-gallon size cans arranged in three rows of 9 boxes. The temperature of45.5° C. (114° F.) was measured at a center can after 28 hours. Insample 13, the pallet was broken down to individual rows of 9 boxes,which were separated so that oven air could circulate among the boxes.After 21 hours, the temperature of 74.4° C. (166° F.) was measured after21 hours.

°T Bact. WPG Visco. ICI pH Gloss Sheen Tint C/R Foam Control RT 3 11.1692 1.3 8.63 1.9 4.5 99.22 0.947 11 12 45.5° C. 0 11.09 91.8 1.15 8.221.8 4.0 101.17 0.947 13 13 74.4° C. 0 11.09 92.1 1.08 8.12 1.8 3.7102.15 0.945 20The end notes for the Table in Example 10A are applicable to the Tablein Example 10B.

Example 11

The experiments from Example 7 for paints without biocides are continuedin this Example. Biocide free paint samples were made and tested free ofbiological agents using the HyCheck method described above. These paintsamples are inoculated with 2% inoculum similar to those used above, andthen incubated for two days at 25° C. to promote bacterial growth. Theinoculated and incubated samples were tested and exhibited a rating of4, i.e., very strong bacterial growth for an additional 24 hour testingperiod at 30° C.

Vials were filled with about 28 grams of the biocide free, inoculatedpaint samples. The vials are further incubated for 1, 2, 3, 6 or 7 daysand then pasteurized in a hot water bath at 60° C., 65.5° C. and 72° C.for various time periods from 0.5 minute to 12 minutes, as shown in thetable below. Control samples without pasteurization are also includedfor comparison. Levels of bacteria and mold were measured using theHycheck tests and reported below.

Incubation time (days) Bacteria Growth Mold Growth ° C. min:sec 1 2 3 67 2 3 6 7 60 2:00 4 4 4 4 0 0 0 60 3:00 3 3 3 3 0 0 0 60 4:00 0.5 1 2 20 0 0 60 4:30 0 0 0 0 0 0 0 60 7:00 0 0 0 0 0 0 0 60 12:00  0 0 0 0 0 00 65.5 1:00 3 3 3 3 0 0 0 65.5 2:00 3 4 4 4 0 0 0 65.5 3:00 0.5 1 2 2 00 0 65.5 4:00 0 0 0 0 0 0 0 65.5 4:30 0 0 0 0 0 0 0 65.5 7:00 0 0 0 0 00 0 65.5 12:00  0 0 0 0 0 0 0 72 0:30 3 3 3 3 0 0 0 72 1:00 4 4 4 4 0 00 72 2:00 0 0 0 0 0 0 0 72 3:00 0 0 0 0 0 0 0 72 4:00 0 0 0 0 0 0 0 724:30 0 0 0 0 0 0 0 72 7:00 0 0 0 0 0 0 0 72 12:00  0 0 0 0 0 0 0 Nonen/a 4 4 4 4 0 0 0

The results show that pasteurization by hot water bath at 60° C. iseffective at about 4.5 minutes, at 65.5° C. is effective at about 4minutes and at 72° C. is effective at about 2 minutes. Based on thetests conducted, the inventors believe that pasteurization at 65.5° C.can be reduced to about 3.5 minutes. The results from this Example 11are compared to those from Example 7, which were pasteurized by heatedair oven.

Pasteurizing Time Temperature (min) (° C.) Pasteurized by 2:00 72 Hotwater 4:00 65.5 Hot water 4:30 60 Hot water 75:00  60 Heated air oven360:00  49 Heated air ovenWhile the results from Example 7 appear to be different than those fromExample 11, the inventors noted that Example 7 utilizes vials holding 52grams of biocide free paints and Example 11 utilizes vials holding only28 grams of biocide free paints.

The difference in the paint mass, i.e., 28 g versus 52 g, and thedifference is pasteurization methods, i.e., hot water bath versus heatedair oven, can account for this apparent difference between Examples 7and 11. The specific heat capacity of air is 1,005 Joules/kg·° C. andthe specific heat capacity of water is 4,186 Joules/kg·° C. The volumeof 1 kg of dry air at sea level and at 15° C. is about 0.816 m³ and thevolume of 1 kg of water at sea level is only about 0.001 m³. Hence, theinformal “volumetric” heat capacity of air is 1,231 J/m³·° C. and forwater is 4,186,000 J/m³·° C. In other words, the volumetric heatcapacity of water is three orders of magnitude higher than that of air.The lag time in the air oven would be significantly longer than in a hotbath.

The inventors note that based on the results presented herein,pasteurization can be carried out by heated air, hot water bath, heatedpipes or vessels that carry or transport the paints or other methodsthat can transfer heat to the paints. The present invention is notlimited to any particular method of heat pasteurization.

While it is apparent that the illustrative embodiments of the inventiondisclosed herein fulfill the objectives stated above, it is appreciatedthat numerous modifications and other embodiments may be devised bythose skilled in the art. One such modification is that paint may beheated to various elevated temperatures during production which includesthe paint making mixing, processing, transfer and filling (of cans orother containers) steps and this exposure to elevated temperatures forvarious times as described above will pasteurize it. Therefore, it willbe understood that the appended claims are intended to cover all suchmodifications and embodiments, which would come within the spirit andscope of the present invention.

We claim:
 1. A method for pasteurizing a paint or stain compositioncomprising the steps of (i) preparing the paint or stain composition,wherein the paint or stain composition comprises latex particles thatwhen applied to a substrate form a paint film; (ii) treating the paintor stain composition with a gamma radiation, wherein an amount ofapplied gamma radiation is less than about 15 kilograys without furtherpolymerizing the paint or stain composition; and (iii) storing thetreated paint or stain composition in containers.
 2. The method of claim1, wherein step (iii) comprises storing the pasteurized paint or staincomposition at temperatures that discourages or inhibits growth ofbiological agents.
 3. The method of claim 2, wherein said temperaturesare temperatures below ambient temperature.
 4. The method of claim 1,wherein the amount of applied gamma radiation ranges from about 3kilograys to about 15 kilograys.
 5. The method of claim 1, wherein theamount of applied gamma radiation ranges from about 5 kilograys to about10 kilograys.
 6. The method of claim 1, wherein the amount of appliedgamma radiation ranges from about 3 kilograys to about 5 kilograys.